Rock anchor



FIG. 1 is a perspective view of a rock anchor showing my new design;

FIG. 2 is a front side view thereof, the rear being a mirror image;

FIG. 3 is a right side view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a top view thereof;

FIG. 6 is a bottom view thereof. 

The ornamental design for a rock anchor, as shown and described. 